A switch device is an essential device in a circuit, which functions to turn on and off the circuit. When the two contacts in a switch device are disconnected, an arc is generated, e.g., a plasma arc column with a conical surface is generated from the combustion at the cathode spot. Especially in a high voltage circuit, the arc generated between the switch contacts is extremely intense.
The arc raises the temperature of the switch, which wears the switch, and the current breaking capability of contacts is decreased because the arc occurs. Therefore, when the switch contacts are turned on and off, the arc-extinguishing process must be performed. In the switch device in the prior art, an arc-extinguishing medium such as oil, sulfur hexafluoride (SF6), air, semiconductor, or vacuum is usually used for performing the arc-extinguishing process. Different arc-extinguishing media have different corresponding characteristics. As the vacuum switch has small gaps between the contacts, high voltage-resistant capability, low arc voltage, high current breaking capability, low electrical erosion, and long electrical endurance, the vacuum switch has been widely applied in various power circuits.
In the prior art, a vacuum switch tube usually includes two contacts sealed in a vacuum shell. Contact bodies of the two contacts respectively include a magnetic member and a conductive member joining and combining with each other. During the current breaking, a distance between the two contacts gradually increases, and a contact area between the contact bodies gradually decreases, until only one contact point is left between the contact bodies. At the same time, a contact resistance gradually increases, such that temperature of the area where the contact point is located gradually rises. Once the temperature is higher than a melting point of the contact point, the contact point is melted, evaporated, and ionized. The metal vapor maintains the discharging in vacuum, so as to generate a vacuum arc. At this time, the key point of the successful current breaking is that an insulation recovery speed at the gaps of the contact bodies is higher than a transient recovery voltage speed at the gaps of the contact bodies after the crossing zero of the arc current, such that re-ignition does not occur and the current breaking is successful. During the current breaking in the vacuum arc-extinguishing chamber, the metal vapor released by the arc diffuses rapidly during the crossing zero of the arc current and is condensed instantly upon encountering surfaces of the contact bodies or shielding case. Therefore, the influencing factors such as size, material, or form of contact bodies, gap between contact bodies, density of the metal vapor generated during current breaking, and density of charged particles need to be designed properly.
Generally speaking, a desirable vertical magnetic field formed between contact bodies through the magnetic members can accelerate the arc-extinguishing process, which can achieve excellent insulation recovery after arcing. However, in the current vacuum switch contacts, due to the restriction of structural shapes, it is usually very difficult to form a desirable vertical magnetic field for performing arc-extinguishing, and it is rather difficult to solve problems such as electric field concentration, insufficient voltage resistance, and high re-ignition possibility during the high voltage breaking process. For a high voltage circuit, the 36-kilovolt voltage breaking can be realized in the prior art. For a higher voltage circuit, particularly, 72-kilovolt high voltage circuit, currently, no vacuum switch tube structure is available for satisfying effective arc-extinguishing requirements during the breaking process. This is one of the problems to be solved in the vacuum switch technology in the prior art.